Peroxygen compositions

ABSTRACT

Storage stable, aqueous acidic solutions having a pH in the range of from 1 to 5 comprising at least one ester peracid having general formula                    
     where R represents an alkyl group having from 1 to 4 carbons and x equals 1 to 4, are provided. The solutions can be prepared by contacting an aqueous solution of a carboxylic compound having general formula                    
     where x is from 1 to 4 and R represents an alkyl group having from 1 to 4 carbons with an inorganic peroxygen compound, preferably hydrogen peroxide, at a pH of less than 4 until at least some ester peracid is produced, and thereafter adjusting the pH to be in the range of from 1 to 5, if necessary.

This invention concerns peroxygen compositions. More specifically, thisinvention concerns solutions of peracids, and still more specifically,this invention concerns solutions of ester peracids.

It is well known that certain classes of compound exert a very strongmicrobicidal effect which renders them suitable for use as disinfectantsin a wide range of applications, especially domestic and industrial hardsurface disinfection. One of the most commonly employed compounds issodium hypochlorite solution, because it is readily available at lowcost and is reasonably effective as a disinfectant over short contacttimes. In recent years, however, there has been increasing concernexpressed at the possible environmental consequences of the use ofhypochlorite solutions, including the possible formation of chlorinatedorganic compounds, such as trihalomethanes, and so attempts have beenmade to identify alternative disinfectants.

One group of chemicals which it has hitherto been proposed to employ asan alternative to hypochlorite disinfectants comprises organic peroxygencompounds, particularly aliphatic C₁ to C₃ peracids such as peraceticacid. Although very effective microbicides, some people find the odourof these aliphatic peracids to be offensive or irritating, and so forapplications in which the disinfectant is likely to be employed in theproximity of people, it is desirable to find alternative disinfectants.

Many disinfectant compositions, particularly household disinfectantsemploy a concentrated solution of disinfectant which is diluted to therequired concentration in use. Many such concentrated solutions employwater as the solvent on account of its low cost, ready availability andease of safe handling compared with organic solvents. It is obviouslydesirable that the disinfectant forms a single phase system in theconcentrated solution because this avoids the need for the solution tobe agitated before use. The formation of a single phase system reducesthe possibility of the disinfectant becoming unevenly distributedthroughout the composition and hence the possibility of inadequate orexcessive dosing of the disinfectant.

Ester peracids are known in the prior art. For example, European Patentapplication No. EP-A-0 166 571 teaches the use of ester peracids of thegeneral formula [RX]_(m)AOOH, where R is hydrocarbyl or alkoxylatedhydrocarbyl, X is a heteroatom moiety, preferably oxygen, A is a widerange of organic moieties containing one or two carbonyl groups and m isone or two, for use in bleaching and laundry applications.

European Patent application No. EP-A-0 426 217 teaches the use of esterperacids of the general formula X-O₂C-A-CO₃H, where A is a C1 to C12alkyl, aryl or alkaryl radical and X is a C1 to C20 alkyl, aryl, alkylaryl radical, optionally including a heteroatom, for use in bleachingand cleaning systems.

Both French Patent application no. 2324626 and a paper by Nedelec et al,Synthesis, 1976, pp821-3 teach a method for the preparation andisolation of ester peracids from the reaction between acid chlorides andhydrogen peroxide in organic solvents.

A paper by C. Lion et al, Bull. Soc. Chim. Belg. 1991, 100, pp555-559discloses the preparation and isolation of ester peracids by thereaction between ester acid and hydrogen peroxide in the presence ofhigh concentrations of sulphuric acid, and quenching into ice. The esterperacids so produced are employed in the destruction of toxicorganophosphorus compounds in aqueous alkaline solution.

None of the prior art references specifically disclose the storagestable, aqueous acidic ester peracid solutions of the present invention,or the use of solutions of such ester peracids as disinfectants.

It is an objective of the present invention to provide novel storagestable, aqueous acidic ester peracid solutions.

It is another objective of the present invention to provide a peracidmicrobicide with reduced odour compared with C1 to C3 aliphaticperacids.

It is yet another objective of the present invention to provide a methodfor preparing storage stable, aqueous acidic ester peracid solutions.

It is a further objective of the present invention to provide a methodfor disinfecting using low odour peracids.

According to the present invention, there are provided storage stable,aqueous acidic solutions having a pH in the range of from 1 to 5comprising at least one ester peracid having the general formula:

where R represents an alkyl group having from 1 to 4 carbons and x isfrom 1 to 4.

According to another aspect of the invention, there is provided aprocess for preparing storage stable, aqueous acidic solutionscomprising at least one ester peracid, characterised in that the processcomprises contacting an aqueous solution of one or more carboxyliccompounds having the general formula:

where x is from 1 to 4, R represents an alkyl group having from 1 to 4carbons and x is from 1 to 4 with an inorganic peroxygen compound at apH of less than 4, preferably 3 or less, until at least some esterperacid has been produced and, thereafter, where the pH of the resultantester peracid solution produced is less than 1, its pH is adjusted to bein the range of from 1 to 5.

A further aspect of the invention provides a method for disinfectingcharacterised in that a substrate to be disinfected is contacted with adisinfectant prepared from a storage stable, aqueous acidic solution ashereinbefore defined.

The aqueous acidic solutions according to the present invention compriseat least one ester peracid defined by having the general chemicalformula:

where R represents an alkyl group having from 1 to 4 carbons and x isfrom 1 to 4. When R has 3 or 4 carbons, the alkyl group can be linear orbranched, i.e. the alkyl group can be n- or isopropyl, or n-, iso- ortertiary butyl. Preferably, R is a methyl group. In many cases, thevalue of x is 2, 3 or 4.

In a particular embodiment, the solution according to the presentinvention comprises a mixture of the ester peracids where x is 2, 3 and4, i.e. a mixture of the monoesters of peradipic, perglutaric andpersuccinic acids. In a particularly preferred embodiment, the majorfraction of the ester peracids present in the composition has x equal to3.

The solutions according to the present invention have a pH in the rangeof from 1 to 5, and preferably from 1.5 to 4. In certain embodiments,the pH of the solutions is greater than 1.75, and may be greater than 2,for example 2.5 or more. A pH in the range of from 3 to 3.5 may beadvantageous in certain embodiments. The ester peracid solutionsaccording to the present invention can often exist as equilibriummixtures in aqueous solution, in which the ester peracid is inequilibrium with water, hydrogen peroxide and the non-peroxidised acid.The equilibrium obeys the following general equation:

where R represents hydrogen or an organic radical. It will be readilyapparent that, for a fixed concentration of one component, the relativeconcentrations of the individual components can vary over a wide rangeand still be at equilibrium. When a solution of an ester peracid is notat equilibrium, chemical reaction takes place such that the compositionof the mixture changes towards that of the equilibrium composition.

The solutions according to the present invention have the advantage ofstorage stability, ie the activity of the ester peracid component of thesolution is retained through extended periods of storage. Depending onthe application, the desired storage stability can range from periods ofseveral days, for example 10 or more days, to periods of several, forexample 4 or more, weeks, and even several, for example, 3 or more,months.

The ester peracids are often present in the solutions, either in use orin storage, at a total concentration of from about 0.0001 to about 15%by weight of the solution, preferably from about 0.05 to about 10% byweight, and more preferably from about 0.1 to about 5% by weight. Itwill be recognised that ester peracid solutions for storage and/ortransportation, particularly where a dilution to produce an in usecomposition will be employed, will often comprise at least 0.1% byweight ester peracid, preferably at least 1% by weight ester peracid.

The total concentration of non-peroxidised ester acids is typically upto about 15% by weight of the solutions, although concentrations of upto 30% can be employed in certain embodiments, often from about 0.05 toabout 10%, most often from about 1% to about 9%.

Hydrogen peroxide is typically present in the solutions at aconcentration of up to 30% by weight, with concentrations in the rangeof from 15 to 25%, for example about 20% by weight, giving particularlygood results in certain embodiments. In other embodiments, theconcentration of hydrogen peroxide is often from about 0.5 to about 15%,more often from about 1 to about 10%.

Optional components in solutions according to the present inventioncomprise stabilisers, inert inorganic salts, surfactants, dyes,perfumes, corrosion inhibitors and, where thickening is not achieved bya combination of components present for other purposes, thickeners. Theoptional components can be present at a wide range of concentrations,but in many cases, the total concentration of these optional componentswill not exceed 25% by weight.

Stabilisers can desirably be employed to improve the storage stabilityof solutions according to the invention and are especially desirablewhere the proposed application involves the likely chance that the esterperacid will be contacted with compounds known to cause decomposition,for example transition metal ions. Suitable chelating agents are oftenaminopolycarboxylic acids or salts thereof such as EDTA or DTPA, and/orcarboxylic acid substituted N-containing heterocyclics, such as8-hydroxyquinoline or picolinic or dipicolinic acid, andorganopolyphosphonates, including hydroxyethylidenediphosphonic acid,and alkyleneaminomethylene phosphonic acids such as ethylenediaminotetra methylene phosphonic acid,cyclohexane-1,2-diaminotetramethylene phosphonic acid anddiethylenetriaminepenta methylene phosphonic acid. A combination of anorganophosphonate and an N-heterocyclic carboxylic acid is particularlysuitable. The amount of chelant in the solution is at the discretion ofthe formulator, but is preferably greater than 0.25% and often notgreater than about 1.5%, calculated as active material therein.

The surfactants which can be employed herein can be nonionic, anionic,cationic, or amphoteric. Generally, the surfactants contain at least onehydrophobic group, e.g. an aliphatic hydrocarbon group containing atleast 8 carbon atoms, and often from 10 to 26 carbon atoms, thealiphatic group often being acyclic, but sometimes containing analicyclic group, or the hydrophobic group can be an alkaryl groupcontaining at least 6 and preferably up to 18 aliphatic carbon atoms.The surfactant contains in addition at least one water-solubilisinggroup for example a sulphonate, sulphate, or carboxylic group which islinked either directly or indirectly to the hydrophobic group. Linkingmembers can include residues of polyhydric alcohols containing ethericor esteric linkages, for example derived from ethylene glycol,propylenie glycol, glycerine or polyether residues. The surfactants canbe soap or be synthetic, for example as described in chapter 2 ofsynthetic Detergents by A. Davidsohn and B. M. Milwidsky, 6th Editionpublished in 1978 by George Godwin Limited, and methods of making themare described in chapter 5 of the same book. Amongst anionic surfactantsdescribed on pages 11-23 of the aforementioned book, sulphonates andsulphates are of special practical importance. The sulphonates include,for example, alkaryl sulphonates, and particularly alkyl benzenesulphonates, the alkyl group preferably being a straight chaincontaining 9 to 15 carbon atoms, of which one of the most commonlyemployed surfactants is linear dodecyl benzene sulphonate. Other anionicsulphonates which are useful in solutions herein include olefinsulphonates, obtained, for example, by sulphonating primary or secondaryaliphatic mono-olefins, alkane sulphonates, especially linear alkanesulphonates, and hydroxy alkane sulphonates and disulphonates,especially 3-, 4-, and 5-hydroxy-n-alkyl sulphonates in which the alkylgroup contains any even number from 10 to 24 carbon atoms. Otherdesirable anionic surfactants include alcohol sulphates, preferablylinear, having a chain length of at least 10 carbon atoms and sulphatedfatty acid alkanolamides. Other sulphates comprise sulphated nonionicsurfactants as for example alkylphenoxyethylene oxide ether sulphate inwhich the alkyl groups contain from about 8 to 12 carbon atoms and thereare 1 to 10 units of ethylene oxide in each molecule. Yet other sulphatesurfactants comprise alkyl ether sulphates where the alkyl groupcontains from 10 to 20 carbon atoms, preferably linearly and eachmolecule contains from 1 to 10 preferably from 1 to 4 molecules orethylene oxide. Further anionic surfactants include phosphatederivatives of the ethylene oxide based nonionic surfactants describedherein.

It is of considerable advantage that at least a proportion of theanionic surfactant be in liquid form or readily liquifiable.

In many suitable classes of anionic surfactants the counter ion is amonovalent metal ion, often a sodium or potassium ion, or a quaternaryammonium cation derived for example from ethanolamine or isopropylamine.

In practice, cationic detergents are normally not present in the samecomposition as anionic surfactants, but when cationic detergents areused they are frequently quaternary ammonium salts such as tetraalkylammonium salts in which at least one of the alkyl group contains atleast 10 carbon atoms or quaternary pyridinium salts substituted by analkyl chain of at least 10 carbon atoms. Although quaternary ammoniumhalides, commonly chlorides, can be employed, particularly where thequaternary ammonium halide and ester peracid are combined shortly beforeuse, in many embodiments it is preferred to employ non-halide quaternaryammonium salts. The use of non-halide quaternary ammonium salts isparticularly preferred where the solution containing the ester peracidand quaternary ammonium salt are to be stored for any significantperiod. The use of quaternary ammonium halides in such solutions forstorage can cause decomposition of the ester peracid by oxidation of thehalide. Examples of non-halide quaternary ammonium salts includesulphates, methosulphates, ethosulphates, hydroxides, acetates,saccharinates, phosphates and propionates.

A considerable proportion of nonionic surfactants suitable for use inthe present invention comprises condensation products of ethylene oxideand possibly propylene oxide. One class of such nonionic surfactantswhich is of special importance comprises water soluble condensationproducts of alcohols containing from 8 to 18 carbon atoms with anethylene oxide polymer often containing at least 5 moles of ethyleneoxide per molecule of surfactants, e.g. from 7 to 20 moles of ethyleneoxide. Other nonionic surfactants comprise water soluble condensates ofalkyl phenols or alkyl naphthols with an ethylene oxide polymer normallycontaining from 5 to 25 moles of ethylene oxide per mole of alkyl phenolor alkyl naphthol. The alkyl group normally contains from 6 to 12 carbonatoms and is frequently linear. As an alternative to the hydrophobicmoiety of the nonionic surfactant being linked to the hydrophilic moietyby an ether link as in alcohol or phenol/ethylene oxide condensates, thelinkage can be an ester group. The hydrophobic moiety is normally theresidue of a straight chain aliphatic acid containing from 8 to 22carbon atoms and more particularly lauric, stearic and oleic residues.In one class of nonionic ester surfactants, the hydrophilic moiety oftencomprises polyethylene oxide, frequently in the ratio of from 5 to 30moles of ethylene oxide per mole of the fatty acid residue. It will berecognised that both mono and di esters can be employed. Alternativelyit is possible to employ as the hydrophilic moiety glycerol, therebyproducing either mono or di glycerides. In a further group, thehydrophilic moiety comprises sorbitol. A further class of nonionicsurfactants comprise alkanolamides which can be obtained when a C10 toC22 amide is condensed with a polyethylene oxide or polypropylene glycolhydrophilic moiety or moieties. Semi-polar detergents include watersoluble amine oxides, water soluble phosphine oxides and water solublesulphur oxides, each containing one alkyl moiety of from 10 to 22 carbonatoms and two short chain moieties selected from the groups of alkyl andhydroxyalkyl groups containing 1 to 3 carbon atoms.

Useful amphoteric surfactants include derivatives of aliphaticquaternary amrhonium, sulphonium and phosphonium compounds in which thealiphatic moieties can be linear or branched, or two of which can jointo form a cyclic compound, provided that at least one of theconstituents comprises or contains a hydrophobic group containing fromabout 8 to 22 carbon atoms and the compound also contains an anionicwater solubilising group, often selected from carboxylic, sulphate andsulphonates.

Non-surfactant thickeners which may be employed comprise cross linkedpoly(acrylates), natural gums such as xanthan or rhamsan gum, cellulosederivatives such as carboxymethyl cellulose and silicates.

The process for preparing storage stable, aqueous acidic solutionsaccording to the present invention comprising at least one esterperacid, comprises contacting an aqueous solution of one or morecarboxylic compounds having the general formula:

where x is from 1 to 4, R represents an alkyl group having from 1 to 4carbons, and x is from 1 to 4, with an inorganic peroxygen compound at apH of less than 4 until at least some ester peracid is formed. Thecontact is normally effected at a temperature of from about 0° C. toabout 50° C., and in many embodiments is effected at a pH of 3 or less,particularly preferably 2.5 or less. Where the pH of the resultant esterperacid solution produced is less than 1, its pH is adjusted to be inthe range of from 1 to 5.

The inorganic peroxide, which is preferably hydrogen peroxide but may bea persalt such as sodium perborate mono and tetrahydrates, can bepresent in an equimolar ratio to the ester acid or acid derivative, butin many cases it is desirable to employ a molar excess of the inorganicperoxide. It will be appreciated that as the solution of ester peracidproduced will tend to form an equilibrium composition, the choice ofconcentrations of the starting materials will to a large extentdetermine the final composition produced, unless subsequent processing,e.g. dilution, cause this to be changed.

In certain embodiments where particularly rapid formation of the esterperacid is desired, the process for preparing storage stable, aqueousacidic solutions according to the present invention can be carried outin the presence of a catalytic amount of a strong acid, for examplesulphuric acid, phosphoric acid and organic sulphonic acids such asmethane sulphonic acid, to increase the rate of formation of the esterperacid by lowering the solution pH. A pH in the range of from 0 to 1 isoften employed. When employed, the strong acids will often be present inan amount ranging from 0.1 to 5% by weight of the solution. However, itwill be recognised that the presence of a strong acid species causesrelatively rapid hydrolysis of the ester function. Loss of the esterfunction not only directly causes loss of ester peracid, but alsoindirectly, by removing ester acid from the equilibrium, which causesester peracid to revert to ester acid and hydrogen peroxide. Therefore,where a strong acid is employed, to produce a storage stable solution ofan ester peracid, the strong acid should be neutralized by the additionof a corresponding amount of alkali. Alkalis that can be employed forthis neutralization include in particular alkali metal hydroxides andammonia, particularly sodium hydroxide. In preferred embodiments of thepresent invention, a strong acid catalyst is employed, and the solutionallowed to react in the presence of the strong acid until the esterperacid concentration reaches the desired concentration. At this point,alkali is then added to raise the pH of the solution to a value wherethe catalytic production of ester peracid is reduced or prevented, andthe hydrolysis of the ester is also reduced or prevented, often a pH inthe range of from 1.5 to 5, and particularly from 2.5 to 4, for examplea pH of from 3 to 3.5.

In another preferred embodiment, the ester peracids according to theinvention are prepared by controlled addition of an aqueous solution ofhydrogen peroxide, having a concentration of up to 90% w/w and oftengreater than about 30% w/w, preferably from about 65% to about 88% w/whydrogen peroxide to an aqueous solution of the ester acid startingmaterial plus any other optional components with gentle agitation.Preferably, ambient temperature is employed, with typical values rangingfrom about 10° C. to about 30° C. The time required to allow the esterperacid solution to reach equilibrium will depend on many factors,including the temperature and the presence and amount of any acidcatalysts employed. Typical times are often between 1 day and about 30days.

In a particularly preferred embodiment, the source of ester acidstarting material comprises a mixture of the monomethyl esters ofsuccinic, adipic and glutaric acid.

In some embodiments of the present invention, the ester acid is obtainedin situ by hydrolysis of a diester, optionally in the presence of theinorganic peroxygen compound. Conditions similar to those employed forthe strong acid catalysed production ester peracid are employed,followed by subsequent addition of alkali to mitigate against thedetrimental effects of the strong acid on the ester function. Theadvantage of such an approach is that it enables the more readilyavailable diesters to be employed as starting materials.

The method for disinfection according to the present invention comprisescontacting the substrate to be disinfected with a storage stable,aqueous acidic solution of an ester peracid, or with a solution preparedfrom one. The solution may be employed without dilution, or may bediluted. When the compositions are diluted, the dilution is usuallychosen to give a concentration of ester peracid in solution of betweenabout 1 part per million and 10,000 parts per million, depending on thesubstrate.

The disinfecting method may utilise a very wide range of temperatures,typically ranging from about 4° C. to the boiling point of the solutionemployed as a disinfectant. In many cases, especially if thedisinfectant is being applied manually using, e.g. a cloth, thetemperature will be limited by the maximum temperature which can betolerated comfortably by the operative, and is unlikely to be greaterthan 60° C.

The disinfection process can be employed to treat a wide range ofsubstrates. Many of the treatable substrates are either liquid or solid.A contaminated gaseous substrate can be treated conveniently by sprayingwith a dilute solution of the invention biocidal combination or bybubbling the gas through a bath of the invention peracid solution. Onetype of liquid substrate comprises micro-organism contaminated aqueousmedia such as recirculating process waters, or aqueous effluents priorto discharge. Such process waters and effluents occur in many differentindustries and can be contaminated by bacteria, algae, yeasts and morerarely by viruses. Without limiting to the following industries,contaminated process waters are prevalent during the processing of plantand animal materials, including the paper and pulp industries, foodprocessing e.g. the sugar refining industry, brewing, wine-making andalcohol distilling industries, effluents from straw treatments,discharges from sewage treatment works, including partially treated ormerely filtered discharges of sewage through pipelines extending out tosea, meat processing factories, carcass rendering activities and fromthe rearing of livestock. Other liquid substrates include irrigationwater in the horticulture industry. A further important source ofcontaminated aqueous media comprises cooling waters either industriallyor arising from air conditioning units installed in large buildings;such as hotels, offices and hospitals. The invention compositions can beemployed to treat non-aqueous liquid media, such as cutting oils.

Notwithstanding the foregoing, the invention compositions are seen as ofparticular value for disinfection in those areas which come into contactwith humankind. Thus they can be employed to disinfect solids, includinghard surfaces, or contaminated articles intended for re-use in the foodprocessing, animal rearing, horticulture, catering, domestic or hospitalenvironments. Hard surfaces can be made from metals, wood, ceramics,glass, and plastics and can include work-benches, walls, floors,sanitary ware, plant or apparatus, containers, tools, machinery, plantand pipework. It will be recognised that for such hard surfaces, it isoften convenient to immerse smaller articles in a solution of theinvention biocidal composition, and for larger applications, a spray orthe like distribution means can be easier to employ. The process canalso be contemplated for disinfecting water absorbent materials such asinfected linen or especially soiled babies' nappies that are often madefrom terry towelling. The invention compositions can be used todisinfect harvested plants or plant products including seeds, corms,tubers, fruit, and vegetables. Alternatively, the invention compositionscan be used to treat growing plants, and especially crop growing plants,including cereals, leaf vegetables and salad crops, root vegetables,legumes, berried fruits, citrus fruits and hard fruits.

It will none the less also be recognised that the peracid solutionsproduced by the invention process may also be employed, if desired, forthe other purposes for which peracids are used, including bleaching oras a bleach additive in washing processes.

Having described the invention in general terms, specific embodimentsthereof will now be illustrated by way of example only.

EXAMPLE 1

Preparation of monomethyl perglutarate (MMPG)

Aqueous solutions comprising 10% w/w monomethylglutarate (MMG) and 10%w/w H₂O₂ (Sample A), 10% w/w MMG and 20% w/w H₂O₂ (Sample B), 20% w/wMMG and 10% w/w H₂O₂ (Sample C), 20% w/w MMG and 20% w/w H₂O₂ (SampleD), 30% w/w MMG and 10% w/w H₂O₂ (Sample F), and 30% w/w MMG and 20% w/wH₂O₂ (Sample E) were prepared by dissolving monomethylglutarate inwater. To this solution was added with gentle stirring, the requiredamount of hydrogen peroxide (85% w/w) over a period of 10 minutes. Thesolutions each had a pH in the range of 1.5 to 2. The solutions werethen stored at ambient temperature for 12 days and analysed by HPLC atintervals during this storage. The HPLC analysis employed an Apexoctadecyl column (25 cm, 5 microns) available from Jones Chromatography.The eluent was 75:25 water plus 0.25% acetic acid:methanol at an elutionrate of 1 ml per minute. Ultra-violet detection at 210 nm was employed.The analysis showed a peak after 6.8 minutes which was attributed tomonomethylperglutarate. To confirm this as a peracid peak, addition ofthiodiglycol to the sample caused this peak to disappear. In addition tothe MMPG, the concentrations of monomethylglutarate (MMG), glutaric acid(GA) and perglutaric acid (PGA) were also monitored. The results aregiven in Table 1 below.

TABLE 1 Analysis of MMPG Samples (All % w/w) Sample Time (days) % MMG %GA % PGA % MMPG A 5 8.8 0.9 0.13 0.17 12 7.85 1.46 0.29 0.4 21 7.6 2.00.15 0.24 B 5 8.1 0.8 0.31 0.73 12 7.09 1.07 0.65 1.2 21 6.86 1.59 0.630.93 C 5 17.3 1.98 0.2 0.47 12 15.84 3.06 0.44 0.66 21 15.1 4.37 0.220.39 D 1 18.5 1.1 trace 0.36 5 15.8 1.58 0.78 1.8 12 13.48 1.98 1.523.02 21 12.56 2.77 1.73 2.92 E 1 27.4 1.65 trace trace 5 26.1 2.58 0.361.0 12 24.2 3.99 0.6 1.23 21 22.8 6.3 0.32 0.64 F 1 27.6 1.56 0.2 0.59 523.6 1.13 1.1 3.1 12 20.3 2.85 2.1 4.77 21 19.59 4.22 2.12 4.05

Analysis of the solutions by titration with ceric sulphate solutionshowed that after 21 days, Sample A comprised 9.7% w/w H₂O₂, Sample Bcomprised 19.5% w/w H₂O₂, Sample C comprised 8.8% w/w H₂O₂, Sample Dcomprised 19% w/w H₂O₂, Sample E comprised 8.5% w/w H₂O₂, and Sample Fcomprised of 17.2% w/w H₂O₂. The results clearly show the storagestability of the solutions according to the present invention. Thestorage stability results for samples B, D and F, ie those samplescomprising about 20% w/w hydrogen peroxide, are particularlyadvantageous.

Comparison 2

Preparation of monomethyl Derglutarate (MMPG) in the presence of strongacid, without subsequent pH adjustment

5.39 g of monomethyl glutarate, 0.59 g sulphuric acid (98% w/w) and0.189 g hydroxyethylidenediphosphonic acid, commercially available inthe UK under the Trade name DEQUEST 2010, were dissolved in 37.59 g ofdemineralised water. To this solution was added with gentle stirring,5.99 g of hydrogen peroxide (85% w/w) over a period of 10 minutes,producing a solution with a pH of about 0.5. The solution was thenstored for 2 weeks at room temperature (ca 20° C.). Analysis of thesolution by the HPLC method given in Example 1 above showed that after 1day, a mixture comprising MMPG and PGA an approximately 1:1 w/w ratiohad been produced. However, after 2 weeks, substantially no MMPGremained. It was also observed that the concentration of MMG in thesolution had significantly decreased, with a corresponding increase inglutaric acid concentration. These results indicated that the solutionwas not storage stable, probably on account of hydrolysis of the esterfunction in both MMPG and MMG.

Example 3

Preparation of MMPG plus Stabiliser

5.39 g of monomethyl glutarate and 0.189 g hydroxyethylidenediphosphonicacid, commercially available in the UK under the Trade name DEQUEST2010, as stabiliser, were dissolved in 37.59 g of demineralised water.To this solution was added with gentle stirring, 5.99 g of hydrogenperoxide (85% w/w) over a period of 10 minutes. The solution was thenstored for about 2 weeks. The solution was found to have no discernibleodour.

Example 4

Preparation of monomethyl Dersuccinate (MMPS)

Monomethyl succinate (5 g) was dissolved in demineralised water (38.7g). To this solution was added 86% hydrogen peroxide solution (6 g) overa 10 minute period with gentle stirring at room temperature and thenhydroxyethylidenediphosphonic acid, commercially available in the UKunder the Trade name DEQUEST 2010 (0.18 g). The solution was allowed tostand for about 2 weeks, and was found to have no discernible odour.

Example 5

Preparation of monomethyl ester peracid from mixture of monomethylesters of adipic, glutaric and succinic acids

Monomethyl glutarate (3.3 g), monomethyl adipate (0.6 g) and 1.2 gmonomethyl succinate were dissolved in demineralised water (38.7 g). Tothis solution was added 86% hydrogen peroxide solution (6 g) over a 10minute period with gentle stirring at room temperature and thenhydroxyethylidenediphosphonic acid, commercially available in the UKunder the Trade name DEQUEST 2010 (0.18 g). The solution was allowed tostand for about 2 weeks and was found to have no discernible odour.

Example 6

Disinfection Trials

The solutions prepared in Examples 3, 4 and 5 were screened for activityagainst bacteria (Pseudomonas aeruginosa and Staphylococcus aureus) anda yeast (Saccharomyces cerevisiae) employing the method described by M.G. C. Baldry in the Journal of Applied Bacteriology, 1983, vol 54, pp417to 423, with a contact time of 5 minutes at 20° C. The pH of thesolutions was varied as detailed in Table 2 below. The solutions wereemployed at 20 ppm peracid avox against the bacteria and at 50 ppmperacid avox against the yeast. Comparative tests were also carried outemploying the same concentrations of peracetic acid by weight preparedby dilution of a peracid solution containing 1% w/w peracetic acid, 6%w/w hydrogen peroxide and 9% w/w acetic acid. The results of the trialare given in Table 2 below. Table 2 also includes comparative resultsunder the same conditions against the yeast Saccharomyces cerevisiae formonoperglutaric acid solution (PGA), monopersuccinic acid solution (PSA)and a solution comprising a 45:27:27 weight ratio of monoperadipicacid:monoperglutaric acid:monopersuccinic acid (AGS).

TABLE 2 Results of Disinfection Trial Logarithmic Reduction Factor Ps.aeruginosa Staph. aureus Saccha. cerevisiae Example pH 5 6 9 5 6 5 6 9 35.0 5.0 5.3 5.4 5.4 5.0 4.3  3.1 4 5.3 5.0 5.1 5.4 5.5 5.1 5.2  3.6 55.0 5.1 5.0 5.5 5.2 (not measured) PAA 5.0 4.9 5.0 5.4 5.0 5.5 5.3  3.0PGA <3.0 nm <3.0 PSA <3.0 nm <3.0 AGS <3.0 nm <3.0 nm = not measured

The results showed that against the bacteria and the yeasts, the esterperacid solutions according to the present invention gave a disinfectionperformance that was broadly comparable to that of peracetic acid. Thegood performance achieved against the yeasts is particularly surprising,given the poor activity of the PGA, PSA and AGS solutions. During thedisinfection trial, it was observed that the odour of the peracetic acidsolution was unpleasant, but that the odour from any of the solutionsaccording to the present invention was not discernible, thusdemonstrating that, on an equivalent performance basis, the compositionsaccording to the present invention demonstrate lower odour.

Example 7

Preparation of monobutyl perglutarate

Monobutyl perglutarate was prepared by the method of Example 3 exceptthat monobutyl glutarate (prepared by reaction between butan-1-ol andglutaric acid at a 1:1 mole ratio) was employed. After standing for 1day, the solution was analysed and found to comprise 0.08% monobutylperglutarate and 10.2% hydrogen peroxide. After 2 weeks storage at roomtemperature, the solution composition was found to be the same, withinthe limits of experimental error. The composition had no discernibleodour.

Example 8

Preparation of monobutyl persuccinate

Monobutyl persuccinate was prepared by the method of Example 3 exceptthat monobutyl succinate (5 g) (prepared by reaction between butan-1-oland succinic anhydride at a 1:1 mole ratio) was employed. After standingfor 1 day, the solution was analysed and found to comprise 0.05%monobutyl persuccinate and 10.9% hydrogen peroxide. After 2 weeksstorage at room temperature, the solution composition was found tocomprise 0.12% monobutyl persuccinate and 10.4% hydrogen peroxide. Thecomposition had no discernible odour.

Comparison 9

Preparation of monooctyl persuccinate

Monooctyl persuccinate was prepared by the method of Example 5 exceptthat monooctyl succinate (prepared by reaction between octan-1-ol andsuccinic anhydride at a 1:1 mole ratio) was employed.

Examination of the solution produced showed that it had formed a 2 phasesystem.

Example 10

Disinfection Trials

The solutions prepared in Examples 7 and 8 were screened fordisinfection activity by the same general method as in Example 6 above.The pH of the solutions was varied as detailed in Table 3 below. Theresults of the trial are given in Table 3 below.

TABLE 3 Results of Disinfection Trial Logarithmic Reduction FactorStaph. aureus Ps. aeruginosa Saccha. cerevisiae Solution pH 5 6 9 5 6 56 9 7 4.0 3.8 3.9 4.2 4.1 >5 <2.5 3.4 8 4.0 3.9 3.9 4.4 3.9 >5 >5 >5 PAA4.1 3.9 3.8 4.3 4.3 >5 >5 <2.5

The results showed that against the bacteria, the ester peracidsolutions according to the present invention gave a disinfectionperformance that was broadly comparable to that of peracetic acid.Against the yeasts, the disinfection performance was again at leastcomparable with peracetic acid, and in the case of the solution ofExample 8 at pH 9, was marlkedly superior to peracetic acid. Thisrepresents surprisingly good performance as>C4 aliphatic peracids areknown to have very poor activity against yeasts. During the disinfectiontrial, it was again observed that the odour of the peracetic acidsolution was unpleasant, but that the odour from any of the solutionsaccording to the present invention was not discernible, thusdemonstrating that, on an equivalent performance basis, the solutionsaccording to the present invention demonstrate lower odour.

Comparison 11

A solution of the same composition as Example 1, sample A was prepared,except that the solution was buffered to pH 4 on addition of thehydrogen peroxide. The solution was observed to contain substantially noester peracid after 14 days storage at room temperature.

Comparison 12

A solution of the same composition as Example 1, sample A was prepared,except that the pH of the solution was adjusted to 0.5 on addition ofthe hydrogen peroxide. The solution was observed to containsubstantially no ester peracid after 14 days storage at roomtemperature.

The results of Comparisons 11 and 12 demonstrate the importance ofcontrol of the pH during the preparation of the compositions accordingto the present invention.

Example 13 and Comparison 14

A parent solution of the same composition as Example 1, sample A wasprepared, except that the solution also comprised 1% sulphuric acid. ThepH of the solution was about 0.5. After 1 day's storage at roomtemperature, the solution was analysed by the HPLC method of Example 1.The solution was divided into 2 portions. In Example 13, the pH of thesolution was increased to be about 2 by the addition of 47% w/w sodiumhydroxide solution. In Comparison 14, the pH of the solution was notadjusted. The 2 portions were stored at room temperature for a further 8days (ie 9 days storage in total). The portions were then analysed bythe HPLC method of Example 1. The results are given in Table 4 below.

TABLE 4 Sample Time (days) % MMG % GA % PGA % MMPG Parent 1 5.69 2.970.94 0.4 Example 13 9 5.67 3.65 0.29 0.39 Comp 14 9 1.9 5.5 2.36 0.21

The results show clearly that after 9 days storage, the solution ofExample 13 retains substantially the same MMPG concentration as theParent solution, whereas that of Comparison 14 had reduced to almosthalf. This demonstrates the advantage of increasing the pH of solutionsprepared by the use of a strong acid catalyst. It also demonstrates thesuperior stability of the aqueous acidic solutions according to thepresent invention.

What is claimed is:
 1. A storage stable, aqueous acidic equilibriumsolution containing a peracid component in solution and having a pH inthe range of from 1 to 5, said peracid component comprising at least oneester peracid having the general formula:

where R represents an alkyl group having from 1 to 4 carbons and x isfrom 1 to 4, said ester peracid being present in an amount of from 0.1%to 15% by weight of the solution.
 2. A solution according to claim 1,wherein the pH of the solution is from 1.5 to
 4. 3. A process forpreparing a storage stable, aqueous acidic equilibrium solutioncomprising at least one ester peracid, which comprises contacting anaqueous solution comprising at least one carboxylic compound having thegeneral formula:

where x is from 1 to 4 and R represents an alkyl group having from 1 to4 carbons, with an inorganic peroxygen compound in the presence of anacid catalyst to produce in said solution, at a pH of less than 1, anester peracid having the general formula:

where R represents an alkyl group having from 1 to 4 cabons and x isfrom 1 to 4, and, after the ester peracid has reached a desiredconcentration, adjusting the pH of the solution to be in the range offrom 1 to
 5. 4. A process according to claim 3, wherein the inorganicperoxygen compound comprises hydrogen peroxide.
 5. A process accordingto claim 4, wherein the hydrogen peroxide comprises an aqueous solutionhaving a concentration of hydrogen peroxide of from about 65% to about88% by weight.
 6. A solution according to claim 1 or 2 wherein x is 2, 3or
 4. 7. A solution according to claim 1 or 2 wherein R is a methylgroup.
 8. A solution according to claim 1 or 2, wherein the esterperacid is present in the solution in an amount 0.1% to about 5% byweight of the solution.
 9. A solution according to claim 1 or 2, whereinthe ester peracid comprises monomethylperglutaric acid.
 10. A solutionaccording to claim 1 or 2, wherein the ester peracid comprisesmonomethylperadipic acid.
 11. A solution according to claim 1 or 2,wherein the ester peracid comprises monomethylpersuccinic acid.
 12. Asolution according to claim 1, wherein the solution comprises from 15%to 25% by weight hydrogen peroxide.
 13. A solution according to claim 1,wherein said solution includes up to 30% by weight of hydrogen peroxide.14. A solution according to claim 13, wherein said solution includes upto 30% by weight of a non-peroxidized ester acid corresponding to saidester peracid.
 15. A solution according to claim 13 wherein saidsolution includes at least one optional component selected from thegroup consisting of stabilizers, inert organic salts, surfactants, dyes,perfumes, corrosion inhibitors, and thickeners, and wherein the totalamount of said at least one optional component is not more than 25% byweight of the solution.
 16. A solution according to claim 1 wherein saidat least one ester peracid comprises a mixture of monoesters ofperadipic, perglutaric, and persuccinic acids.
 17. A solution accordingto claim 1 wherein said at least one ester acid is generated in situ byhydrolysis of a diester.
 18. A solution according to claim 1 whereinsaid ester peracid is present in an amount of at least 1% by weight ofthe solution.
 19. A process for the storage of a aqueous acidicequilibrium solution containing a peracid component, said peracidcomponent comprising at least one ester peracid having the generalformula:

where R represents an alkyl group having from 1 to 4 carbons and x isfrom 1 to 4, said ester peracid being present in an amount of from 0.1%to 15% by weight of the solution, said process comprising storing saidsolution at a pH of from 1 to
 5. 20. A process according to claim 19wherein said storing is performed for a period of at least 10 days. 21.A method for disinfecting which comprises: providing a storage stable,aqueous acidic equilibrium solution containing a peracid component insolution and having a pH in the range of from 1 to 5, said peracidcomponent comprising at least one ester peracid having the generalformula:

where R represents an alkyl group having from 1 to 4 carbons and x isfrom 1 to 4, said ester peracid being present in an amount of from 0.1%to 15% by weight of the solution; diluting said storage stable solutionto produce a dilute aqueous solution containing said ester peracid insaid dilute aqueous solution in an amount of from 1 to 10,000 ppm; andcontacting a substrate to be disinfected with said dilute aqueoussolution.
 22. A method according to claim 3 wherein said ester peracidis present in said solution in an amount of up to 15% by weight of thesolution.
 23. A method according to claim 3 wherein said catalystcomprises a strong acid in an amount of from 0.1 to 5% by weight of thesolution.
 24. A method according to claim 3 wherein said adjusting thepH of the solution comprises adding alkali to the solution to adjustsaid pH to be in the range of 1.5 to
 5. 25. A method according to claim24 wherein said pH is adjusted to be in the range of 2.5 to
 4. 26. Amethod according to claim 24 wherein said pH is adjusted to be in therange of 3 to 3.5.